1. Field of the Invention
The present invention relates generally to turbochargers with variable geometry. More particularly a turbocharger is provided having a turbine intake with a variable nozzle with sliding blades, with the blades entering via a heat screen of slotted sheet metal suspended in the housing of the turbine and having the turbine wheel embedded therein in order to provide an aerodynamic surface directing the flow of exhaust gas in a turbine wheel with a substantially complete rear disc, an aerodynamic shield and an uncoupled axial actuating device to facilitate mounting.
2. Description of the Related Art
High-output turbochargers use variable-geometry systems for the turbine nozzle intakes in order to increase the performance and aerodynamic yield. Variable-geometry systems for turbochargers have typically been of two types: a type with rotating blades and a type with a piston. The rotating blade type exemplified in U.S. Pat. No. 5,947,681, entitled PRESSURE BALANCED DUAL AXLE VARIABLE NOZZLE TURBOCHARGER provides a plurality of individual blades placed in the intake nozzle of the turbine, which can turn in order to reduce or increase the area of the nozzle and the flow volume. The piston type, which is exemplified in U.S. Pat. Nos. 5,214,920 and 5,231,831 both entitled TURBOCHARGER APPARATUS, and U.S. Pat. No. 5,441,383 entitled VARIABLE EXHAUST DRIVEN TURBOCHARGERS uses a piston or a cylindrical wall which can be displaced concentric to the axis of rotation of the turbine in order to reduce the intake area of the nozzle. In most cases the variable-geometry turbocharger of the piston type includes blades with a leading edge which is fixed with respect to the flow of air, which are either mounted on the piston or on a stationary nozzle wall facing the piston and which enter into slots in the opposite surface during displacement of the piston.
In variable-geometry, piston-type turbochargers of the prior art the challenge has been to maximise the aerodynamic performance balanced by the tolerancing of the contact surfaces, principally of the blades and the reception slots which are subjected to an extreme temperature variation and to mechanical stress, as well as to provide a means for actuating the piston according to a configuration which can be easily manufactured.
A turbocharger incorporating the present invention has a casing having a turbine housing receiving exhaust gas from an exhaust head of an internal combustion engine at an intake and having an exhaust outlet, a compressor housing having an air intake and a first volute, and a central housing between the turbine housing and the compressor housing. A turbine wheel is mounted in the turbine housing to extract the energy from the exhaust gas. The turbine wheel is connected to a shaft which extends from the turbine housing through a shaft bore in the central housing and the turbine wheel has a substantially complete rear disc and multiple vanes. A bearing mounted in the shaft bore of the central housing supports the shaft for rotational movement and a vane wheel is connected to the shaft facing the turbine wheel and enclosed in the compressor housing.
A substantially cylindrical piston is concentric to the turbine wheel and can be displaced parallel to an axis of rotation of the turbine wheel. A plurality of blades extend substantially parallel to the axis of rotation from a first end of the piston in the proximity of the rear disc. A heat screen is engaged at its external circumference between the turbine housing and the central housing and extends radially inwards towards the axis of rotation. The rear disc of the turbine wheel is embedded in the heat screen for the smooth flow of exhaust gas in the vanes. The heat screen also has a plurality of slots receiving the blades. An actuating device is provided to displace the piston from a first position in which the first end is in the proximity of the heat screen to a second position in which the first end is remote from the heat screen.